Abstract: A dry wall building system comprises courses of building blocks where the building blocks are joined end to end by keys. Each of the blocks comprising sidewalls, endwalls and at least one vertical cavity or slot, at least one first channel in the upper surfaces of the endwalls and at least one second channel in the lower surfaces of the endwalls, the arrangement and construction being such that when blocks are laid one upon another the channels and the said at least one cavity or slot of the blocks can be aligned to provide an internal network of horizontal and vertical infill passages which can be filled with a settable material to seal joints between the blocks and to provide load bearing support between respective courses of blocks. A method of manufacturing blocks is also disclosed.